lei q: emit progress and counting via PktOp

lei q: emit progress and counting via PktOp

Sometimes it can be confusing for "lei q" to finish writing to a
Maildir|mbox and not know if it did anything.  So show some
per-external progress and stats.

These can be disabled via the new --quiet/-q switch.

We differ slightly from mairix(1) here, as we use stderr
instead of stdout for reporting totals (and we support
parallel queries from various sources).